INA225-Q1: Accuracy influenced by Vs and Vcm

Hello Sheldon,

Yes, the Vs and Vcm of INA225 will influence its accuracy by the specs known as Power-supply rejection ratio (PSRR) and Common-mode rejection ratio (CMRR). You can learn more about these on the TI Precision Labs videos for PSRR and CMRR.

The maximum PSRR of INA225 is ±1 uV/V. That means for every 1 V that Vs changes from the nominal of 5 V, the input offset voltage (Vos) will change by 1 uV.

For example, if Vs = 12 V, an additional offset voltage of 7 uV will be created at the INA225 input. The impact on accuracy in this case will depend on the sense voltage applied to the device. Unless very small currents are being measured, the sense voltage should be in the tens of mV range and will not be affected much by the PSRR.

The minimum CMRR of INA225 is 95 dB, or 18 uV/V. This works in much the same way as PSRR. For every 1 V that Vcm changes from the nominal of 12 V, the input offset voltage (Vos) will change by 18 uV. As you might guess, this will have more of an impact on accuracy since the offset generated is larger.

If you have more specific conditions, I can provide a more specific error analysis.

Best regards,

Ian Williams
Applications Manager
Current Sensing